5A

🔹 Levels of Structural Organisation

Analogy: Compared to a school building:

• Cells are the basic unit of structure and function.

• Tissues are groups of similar cells.

• Organs are composed of multiple tissue types working together.

• Systems are collections of organs coordinating to carry out major functions.

🔹 Four Basic Tissue Types in Animals

1. Muscle Tissue

   • Striated (skeletal):

     • Voluntary control.

     • Attached to skeleton.

   • Smooth:

     • Involuntary control.

     • Surrounds internal organs.

   • Cardiac:

     • Involuntary control.

     • Found only in heart walls.

2. Nervous Tissue

   • Comprised of:

     • Neurons (transmit signals).

       • Bipolar interneuron

       • Unipolar sensory neuron

       • Multipolar motor neuron

     • Glia (supporting cells; outnumber neurons 10:1).

       • Astrocyte

3. Epithelial Tissue

   • Forms body interfaces:

     • Epidermis (skin).

     • Mucous membranes.

     • Lining of GI tract, airways, reproductive system.

     • Exocrine glands.

4. Connective Tissue

   • Characterised by cells embedded in an extracellular matrix.

   • Types include:

     • Loose connective (areolar).

     • Adipose.

     • Dermis of skin.

     • Ligaments & tendons.

     • Cartilage & bone (osseous tissue).

     • Blood.

🔹 Organs

• Composed of multiple tissue types, typically all four.

• Work together to perform specialised functions.

• Example given: Small intestine (contains epithelial, connective, muscle, and nervous tissues).

🔹 Organ Systems

• A system = group of organs performing a major biological function.

• Major human systems listed:

  • Respiratory

  • Digestive

  • Musculoskeletal

  • Circulatory

  • Lymphatic

  • Immune

  • Excretory

  • Endocrine

  • Nervous

  • Integumentary (skin)

  • Reproductive